Engineers and designers spend their working lives ensuring that bridges are safe. Your brain doesn't always appreciate this, however, and sometimes for very good reasons. These are the ten scariest bridges in the world as chosen by Jalopnik readers.

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Why it's so scary: Investment in American infrastructure is unfortunately not a major priority in these budget-conscious times. And maintaining what exists is much less sexy than planning and building something new. The result is a bunch of rust, chipping concrete, and anxiety-induced indigestion.

Why it's so scary: Two things: First, no bridge on Earth has a greater gap between anchorages. That's a lot of steel and concrete being held up there. Second, the Mackinac has a reputation for letting traffic be blown off the bridge into the Strait below. A Bronco went over the railing in 1997, but that was ruled a suicide; most believe that the Yugo that took the dive in 1989 was simply lifted and tossed over like a toy.

Why it's so scary: Many people have a fear that when they drive over a bridge, they'll end up in the water. This engineering masterpiece makes sure you do that, if in a controlled and dry manner. Also: twenty-three friggin' miles.

Why it's so scary: A civil engineer's dream, an acrophobe's nightmare. This minimalist creation has been carrying four lanes of the A75 autoroute through the air above the River Tarn valley since late 2004. There are longer bridges and higher bridges, but few (if any) combine the two to this degree.

Why it's so scary: The Quepos Bridge is here to proudly represent every creaky battered decayed bridge in the Third World that looks incapable of supporting a bicycle. Still, untold thousands of these rickety structures carry traffic every day, doing their part to make a harsh existence more convenient. And exciting.

Why it's so scary: Many people give Danish philosopher Søren Kierkegaard credit for inventing existentialism; he would appreciate this bridge, further north in Scandinavia, that feels like no less of a leap into the unknown.

Why it's so scary: Galloping Gertie opened for traffic on July 1, 1940, as the third-longest suspension bridge in the world, and a 40-mph wind tore it apart just over four months later. The lessons learned from the experience revolutionized bridge-building.

If you have ever taken an engineering-related college course –statics, materials, even just a good first-semester physics class – the YouTube clip above is going to be six minutes of the most terrifying video you will ever watch.